Allen Bradley

Hi everyone,
This should be a simple one. I am working on a project with an SLC5/03 and 2 Panelview screens. Both screens will share a lot of the same functions, which will consist of momentry pushbuttons. My question is, can I use the same bit for each function on the two screens or do I have to use a seperate bit for each screen?

While I'm here I might as well bring up the dreaded PID instruction. The project I am working on will control a lot of heating. Some of the valves are 0-10v, so these I am using PID to control the output. The other valves are just 2 position sprung return. Would I gain anything having these PID controlled?

Thanks everyone
Dave

You could but should you?

Since you are using momentary buttons you should be able to use the same addresses, but I think it’s a bad idea. It would make the initial programming simpler….but the poor guys who have to troubleshoot the system over the next ten years will all curse you.

First Question:

Yes, the panelviews can have the same address for the functionally same buttons. The Panelviews only write their tag to the SLC when their internal database has changed.

You might get some quirky results if you have have the Write Tag and the Indicator Tag as the same tag. When PV1's button is pushed, the tag will change. PV2 will see that change, and the button object will indicate that it has changed. It will look as though the button is being pushed, without someone there pushing it. I don't consider this a bad feature, but some might.

Second Question:

It depends.

The output of a PID is a number (0 to 100%). How can you control an ON-OFF (e.g. '0' or '1')? The classic method is to have the valve open for X% of a time frame, with the X% being driven by the PID block. Ideally, the time frame would be the same as he PID's update time.

But the real question is: Is there any benefit to cycling these valves open and closed? It's impossible to answer without knowing something about the process and the configuration of the valves. Is a critical process variable affected by the amount of time that one of these valves is open? If yes, then you might need PID control (although ON-OFF with deadband might suffice - even for your control valves). If the valves don't directly affect the temperature, you should not even consider PID for them).

KMG said:

….but the poor guys who have to troubleshoot the system over the next ten years will all curse you.

Click to expand...

KMG -

You mean that you would rather have this:

      PanelView_1      PanelView_1  PanelView_2

       Start            Stop          Stop        MOTOR

---+------| |------+-----|/|----------|/|----------( )-

   |               |

   |  PanelView_2  |

   |   Start       |

   +-----| |-------+

   |               |

   |    MOTOR      |

   +-----| |-------+

than this:

      Start from      Stop from

      PanelView(s)    PanelView(s)   MOTOR

---+------| |------+-----|/|----------( )-

   |               |

   |    MOTOR      |

   +-----| |-------+

?

I don't see where it makes that much difference. The second one is easier to read, and maintain, I think, both from a PLC standpoint and a Panelbuilder standpoint.

The same button on the same screen writes to the same address. That doesn't sound that bad. If there's a downside I'm missing, please let me know - I've been doing it the other way for years.

Wouldnt be any different than having multiple physical start pushbuttons on a machine, depends on the system how that works out. I have dealt with that for many years, at least using an HMI like a panelview it only has to address one bit with either pushbutton similar to systems that parallel hardwire pushbuttons.

I think in the plc/digital world that is called an OR condition but using the panelview/hmi you actually dont have to create it in the code, as Allen pointed out.

Hi Dave I did a similair job myself a few weeks ago. I used different address for each additional button on the new PV. I am only a novice programmer though and while this is my personal style the other lads who replied are the real pros so their example is a good practice to follow.

Hi Dave

If we lived in a perfect world and the PLC was a perfect machine I might consider using a single contact to represent two PanelViews.

The fact is Allen-Bradleys addressing scheme will not allow you to do this, you can't have two devices sharing the same address. You will find it to be (EITHER OR), not both at the same time. Each rack must have its own address. The two PanelViews can share the same internal file addressing but NOT the same discrete or communtcation addressing.

Look at the sketch above and think PLC. It can't work.
It is NOT the same as Real World wiring.

You MUST use separate addressing.

Right or wrong Guys?

Good luck
Roger

Hi Dave
Guess I may be a little late with info, you probably know by now that you can't do that with the pushbuttons.
Sorry bout that.
Roger

Roger I believe you're wrong I have no problem changing the state of a Maintained PB. from the data table in the plc . Is there a difference between that and 2 panelviews . I think you need to remember that the panelview is just reading the tag to display the current state the only time it writes is when the button is pushed.


Seems like its similiar to being able to control the screen that is up from the plc.


I may be wrong if I am please prove it to me.

Drewcrew6

Drew

Allen-Bradley PLCs can not communicate to two devices with the same address, that is just the way it is.
The PLC will look at the first PV that initiates and ignore the other. (Try it.)
You may be able to manipulate the bit in the data table but that is not what I am saying. I am saying that PanelView No.1 can not have the same I/O address as PanelView No.2.
The PLC data table bits are not the same as a real world device, even though you say it is only a momentary button, it still is controlled by the PLC. If the button is open the PLC is holding that button open, if the button is closed, the PLC is holding that button closed.

(The bit that you are manipulating program that bit into a rung of logic, place the PLC in the RUN mode. Bet you can,t manipulate now. The PLC is going to keep that bit in the condition that you have it programmed.

I will not need to prove it to you if you just think about it for a little while. EACH PANELVIEW MUST HAVE ITS OWN AND UNIQUE ADDRESS.

If you still have doubt, we will talk more.
Roger

You are both right and wrong!

Back in the early days, Panelviews were strictly a remote I/O device. They showed up in the I/O image table, and, so therefore, yes, like any other I/O, had to have different addresses.

But....

Even back then, you could Block Transfer data to/from them (just as you block transfer data to/from analog modules). The SOURCE of the Block Transfer Write, or the DESTINATION of the Block Transfer Read, is going to be some internal N: address, and those COULD be the same.

Now-a-days, Panelviews are not usually RIO devices, and you no longer address screen animations based on the internal panelview memory location (Slot 3, Bit 4). They work more like SCADAs in that they use tags, and usually read the PLC directly themselves, rather than being driven by the PLC's scanner.

Therefore a Panelview can read from and write to any address in the PLC. And two Panelviews can read from and write to the same address, if you want them to.

You are right in what yu are saying about both panelviews being able to read and write data to the same file. That is not what I was trying to say, I contend you can not program two panelviews with the same address, whether it be RI/O, DH+ or Ethernet.

A-B PV1400e is the last model I programmed, on the other hand I programmed the origional A-B PLC, the one that had modules that were about 1'x2'x21/2". yes that is approx. one foot deep x two feet tall x two and one half inches wide.

If I press a stop button on one panelview, the PLC is going to see a command to STOP from one PV but see a command NOT to STOP from the other pv. (Same Bit?)

What PanelView model can do this?
What means does it communicate with the PLC?

I know a company called IDT had a Panelmate that acted as an extended data table of the PLC. They came out with that about the time A-B came out with the 1400e.

No we are not both wrong.

You are just bringing out points that were not being discussed.
Chop****Chop.

Even though one could block transfer data from two, three or four panelviews to the same PLC data file, you could not address both panelviews with the same address. Even with block transfers writing/reading the same data table would not work in this situation. One BTW would over write the other BTW with each scan. I don't see the logic in doing such a thing.

Being able to write to the same PLC data table from any number of HMI devices should be common knowledge to a PLC user. The point is is it good practice to have two or more panelviews writing to the same PLC data table. The correct answer is NO. I also don't like indirect addressing and other hidden functions, I like to keep it simple.

I'm a simple kinda guy.
P.S. what model PV are you talking about?

Roger, I think there is confusion here about what is meant by "address". In your case you are talking about the CPU address and the PanelView addresses on the communications network. You are absolutely correct in saying that each device on a communications link must have its own unique address.

What Allen and Dave were taliking about was the memory adress or identification of the bit within the PLC program and the Panelview tag base. That "address" can be used any number of times by any number of devices.

Tom

Thanks, sounds like it.

I still don't see how the PLC will distinguish between panelview stop buttons. One will say open the circuit while the other will say keep the circuit closed, same time, same bit????


have a good day you guys
Roger